In a CMOS and others in recent years, greatly reducing a thickness of an oxide film, e.g., reducing a thickness of a gate oxide film to several nm has been demanded. In such a thin oxide film, irregularities on a wafer surface are similarly transferred as irregularities of the oxide film even after the oxide film is formed.
Therefore, degradation in GOI that is not detected when GOT evaluation is measured in a conventional wafer having an oxide film thickness of 25 nm (an SEMI standard) is detected in such a thin gate oxide film as described above. In regard to the GOI, since uniformity is improved as flatness of a wafer surface is increased, the wafer surface must be flattened as much as possible (see Japanese Patent Application Laid-open No. 6-140377).
For example, the GOI of a wafer that is measured in an oxide film of 10 nm or below is dependent on surface roughness, and a wafer is considered to have no degradation in GOI when an Ra value measured by an AFM (an atomic force microscope) is not greater than 0.1 nm.